class_docstr: Computes mean metric.
class_docstr_tok: ["Computes","mean","metric","."]
code: def extract_output(
      self, accumulator: _Accumulator
  ) -> Dict[metric_types.MetricKey, float]:
      if accumulator.count == 0.0:
          return {self._key: float("nan")}
      return {self._key: accumulator.total / accumulator.count}
  
file_path: model-analysis/tensorflow_model_analysis/metrics/stats.py
imports: import dataclasses
  from typing import Any, Dict, Iterable, Optional, Tuple, Union
  import apache_beam
  from tensorflow_model_analysis.metrics import metric_types
  from tensorflow_model_analysis.utils import util
label_desc: Use image node_id 5 for calling the _MeanCombiner obj's underlying member method code with example usage: obj.extract_output(accumulator) and returns: dict, dict